Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
One of my favorite spring flowers is columbine. I love their clover like foliage and their uniquely shaped flowers. But having columbine means having leaf miners.
What are Leaf Miners?
Leaf miners are the larvae of various insects including flies, sawflies and moths. The larvae overwinter in the soil of your garden and emerge in the spring as young adults. The females lay up to 250 eggs on the undersides of leaves. They use their ovipositor to pierce the surface of the leaves and deposit their eggs inside of the leaves.
The eggs usually hatch within 10 days and the resulting larvae begin to tunnel inside the leaves creating the characteristic wavy lines that you see on your leaves. The larvae live and eat inside the leaf for 2 to 3 weeks before they mature. As the larvae grow, the width of the tunnels increase.
At maturity, they drop to the ground beneath the plant, burrow 1 to 2 inches into the soil and pupate. 15 days later, they emerge as adults and the cycle begins again. It is possible to have multiple generations of leaf miners during the growing season.
What Plants Do Leaf Miners Like?
Leaf miners like broad leaf plants including ornamentals such as my beloved columbine. Citrus trees and blackberries are also on their menu. They cause the most trouble in the vegetable garden where they infest beans, cabbage, lettuce, tomatoes and peppers. They are a big problem for farmers as well as gardeners.
Why Are Leaf Miners So Hard To Kill?
Leaf miners are difficult to kill because they live inside of the leaves of your plants. Spraying your plants doesn’t harm them because the spray only coats the outsides of the leaves. Systemic insecticides which are absorbed by the plants and can kill the leaf miners either contain ingredients that are banned in some areas or are not allowed to be used on edible plants.
Fortunately, there are some simple organic solutions that can help keep your garden free of these pests.
Kill Leaf Miners by Squeezing the Leaves
Keep a careful watch on your plants. As soon as you see the beginnings of the distinctive wavy lines, squeeze the leaves. This will squish the larvae, killing it. This is a great solution because you get the satisfaction of killing the bug without having to actually touch it.
Remove Infected Leaves
If you only have a few leaves with leaf miner damage, you can break off those leaves and discard them. Don’t put them in your compost. Put them in your garbage.
Also carefully check any new transplants before planting them in your garden. If you see any evidence of leaf miner activity, either remove those leaves or return the plant to the nursery from which you bought it for a refund. It’s always a good idea to check plants before you purchase them for any evidence of pests.
Use a Trap Crop
Trap crops are a great way to keep leaf miners out of your valuable plants. Trap crops are plants that are also attractive to a pest. The idea is to plant the trap crop nearby so that the pest infests the trap crop instead of your crop. Good trap crops for leaf miners are columbine, lambsquarter and velvetleaf (a large annual plant that is a member of the mallow family).
A great way to keep leaf miners out of your garden is to stop them from getting in. There are two effective methods that you can use. Many vegetable gardeners and farmers use black plastic to cover the soil in their crop rows. This prevents the hibernating larvae from emerging from the soil in the spring. The plastic prevents any mature larvae that have developed in leaves from dropping to the ground and burrowing into it to finish pupating thereby disrupting the life cycle of leaf miners.
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Another useful barrier is floating row covers. Since the adults are all flying insects, row covers prevent the females from landing on your plants to deposit their eggs. Make sure that you secure the sides and ends of your tunnels to the ground to keep the insects out.
Use Beneficial Insects
Beneficial insects are a great organic solution. For leaf miners, you want to purchase and release a parasitic wasp known as the leafminer parasite. The adults get into the tunnels that leaf miners have created in the leaves and kill them. Then they lay a single egg in the tunnel which hatches into a pupae. The pupae feeds on the dead leaf miner larvae, while it develops into an adult wasp.
Use Sticky Traps
Beneficial insects work great in greenhouses. Another good solution for plants grown indoors or in greenhouses are sticky traps. Sticky traps are cards that are covered with adhesive that are either hung or placed on stick holders in the greenhouse. They are brightly colored because each type of pest is attracted to certain colors. For leaf miners, use yellow or blue. The adults are attracted to the yellow or blue. When they land on the card, they become stuck on the adhesive so that they are unable to mate and then land on your plants to lay their eggs.
Questions & Answers
Question: Is there an essential oil or something from the kitchen to kill this?
Answer: Unfortunately, essential oils and other products that are sprayed on plants don't get rid of leaf miners because they only coat the surface of the leaves while the leaf miners live inside the leaves. You need something that can get inside of the plants to kill the insects. I'm not sure which plants you have that are infected, but I do suggest 6 different ways to kill leaf miners that don't involve chemicals. I'm an organic gardener and use no chemicals in my garden.
Question: If my tomato plants have leaf miner damage will they still produce tomatoes?
Answer: Yes, you will still get tomatoes. Leaf miners do not kill the foliage, just damage it. The plants are still able to photosynthesize and produce foliage, flowers and fruit.
Question: Which systemic insecticide can eradicate leaf miners?
Answer: I cannot answer your question because I am an organic gardener. I don't use pesticides, herbicides or chemical fertilizers. Please remember whenever you use an insecticide, you are using poison. That poison will not stay confined to the plants you are spraying. It spreads throughout the environment and poisons our soil, air, and water. When you use insecticides, herbicides and chemical fertilizers you are poisoning the planet.
Question: I am looking to prevent any leaf miners on my Virginia creeper and grape vines this year, can I spray neem oil solution or protect the soil somehow from them ever getting started?
Answer: Sprays are not going to work against an insect that is living inside of the leaves. Treating your soil won't help because the insects don't ever come in contact with the soil. Try planting a trap crop of columbine, lambsquarter or velvetleaf (a large annual plant that is a member of the mallow family) to lure the insects away from your Virginia Creeper and grape vines.
Question: I wasn't specific enough when asking if it was OK to eat leaves with minor damage. I'm guessing it's leaf miners: there isn't a tunnel in the leaf (though there are a few tunnels on adjacent tulsi leaves. What I see is clusters of tiny white dots, sometimes scattered over the leaf and occasionally lining up but not in the broad curving line associated with leaf miners. I have a HUGE crop of holy basil that I hate not being able to use?
Answer: If the eggs are on the outside of the leaves, it is not leaf miners. Leaf miners lay their eggs inside of the leaves.
Question: I noticed I had what I think are these, I killed the insect inside the leaves and removed affected. Will spinach and chard leaves only slightly eaten by leaf miners still be OK to eat?
Answer: Yes, you can eat leaves that have minor damage. It is recommended that you cut out the damaged part of the leaf before eating, but if you accidentally eat the damaged part, it won't harm you.
Question: Is it okay to eat lightly damaged leaves?
Answer: I don't recommend eating leaves that have leaf miner damage. The larvae live in the tunnels, eating their way through the leaves. That means that they are also excreting in the tunnels. I don't think anyone wants to eat insect droppings!
Question: Will boxwood leaf miners continue to live in cut foliage?
Answer: Yes, because the larvae live inside the leaves. If you are having a problem with leaf miners, do not use any infested cut foliage for floral arrangements. Discard it instead.
Question: Should I cut back my plant in the fall to get rid of leaf miners?
Answer: Cutting back your plant in the fall will not prevent leaf miner infestation because the insects hibernate in the soil of your garden during the winter. Only cut back your plant in the fall if it is a perennial which dies back to the roots in the fall. It is always a good idea to rid your garden of any dead plant material for the winter. If your plant is a perennial which doesn't die back to the roots in the fall, you should not cut it back. Doing so will kill the plant.
© 2018 Caren White
Caren White (author) on August 22, 2020:
That is an excellent question! You should never re-use potting soil for the very reason that you cite: you can pass on disease, insect eggs, mold and fungi to new plants if you re-use the soil. Always use fresh potting soil when you plant your containers. It's also a good idea to clean and sterilize your containers before you re-use them for the same reasons.
Colleen on August 21, 2020:
I removed my potted plant that was overrun with leaf miners. Do I need to dump all the soil in the pot, or can I replant. I'm suspecting if the larvae are in the soil, I'll need to toss it all. Is that so?
Caren White (author) on July 15, 2020:
You're welcome! Glad to be of help.
Virginia Allain from Central Florida on July 14, 2020:
This is great information and I'll start right away pinching the leaves of my yellow squash which is where I'm seeing the leaf miner tracks. Thanks so much.
Caren White (author) on June 18, 2020:
The plastic sold for agricultural and home gardening use is black. Other than warming the soil in the spring, I don't know why it is black.
Ellen on June 18, 2020:
And why specifically black plastic on the soil under leaves of a plant with leaf miners?
Ellen on June 18, 2020:
My Gerbera daisy has leaf miners. Will be trying the black plastic because I have lots of lizards & don't want to hurt them.Thanks for all the info & tips.
Caren White (author) on May 22, 2020:
So glad you found it helpful.
Denise Wetmore on May 21, 2020:
This was very helpful information. Thank you!
Caren White (author) on July 05, 2018:
Glad you found it helpful!
Mary Norton from Ontario, Canada on July 05, 2018:
I don't really have a big garden but who knows when the issue of leaf miners will come up. But my niece who has a huge garden can use these ideas.